Polymeric substrates containing aromatic moieties, such as for example adhesives or coating resins based on aromatic epoxides, aromatic polyesters or aromatic (poly-) isocyanates are highly sensitive to UV/VIS radiation up to wavelengths of approximately 420 nm.
The protection of such adhesive or coating layers with a UV absorbing layer on top is extremely difficult, since already very small amounts of radiation—even in the range of around 410 nm—penetrating the UV absorbing top coating are sufficient to cause delamination and peeling off of the protective coating.
Typical applications, in which long wavelength shifted UV absorbers are extremely useful, are automotive coatings.
Today's automotive coatings have applied an anticorrosive cathodic electro coat directly on the steel plate. Due to the significantly red shifted light sensitivity of the cathodic resins (up to approximately 400-420 nm) it is not possible to protect the cathodic electro coat with conventional prior art UV-absorbers in the top coatings adequately.
In order to better protect such sensitive layers, attempts have been made to shift the UV absorption of triazines towards longer wavelengths. For example, U.S. Pat. No. 5,354,794, U.S. Pat. No. 5,476,937 and U.S. Pat. No. 5,556,973 describe red-shifted hydroxyphenyl triazines.
A few tris(hydroxyphenyl) triazines are described in CAN 81:152177, CAN 118:240480, CAN 135:296246, EP 762197 A, GB 975966 and WO 94/05645 and transition metal complexes of such triazines are described in GB 1294322.
However, the instant compounds may absorb a greater amount of light up to 420-450 nm, in particular up to 420 nm, than the state of the art. The compounds remain unexpectedly photochemically stable and show virtually no migration in typical coating applications.